Conventionally, as a device for supporting a crankshaft 1 of a car shown in FIG. 1 and the like, a split type roller bearing is used in general. Since the roller bearing has high load capacity, it is suitable for a bearing used under high load circumstances.
However, as a fuel-efficient car is increasingly demanded in view of environment, a needle roller bearing is used instead of the roller bearing recently in some cases. As compared with the roller bearing, although the needle roller bearing is low in load capacity, since its friction resistance is low at the time of rotating, its rotation torque or a feeding amount to a supporting part can be reduced.
However, a needle roller bearing to support a crank pin 2 of the crankshaft 1 cannot be press-fitted in the axial direction. Therefore, a needle roller bearing to be used in such place is disclosed in U.S. Pat. No. 1,921,488, for example. According to this document, as shown in FIG. 2, since a needle roller bearing 3 comprises an outer ring having outer ring members 4a and 4b split by split lines extending in an axial direction of the bearing, it can be set in the crank pin 2.
In addition, as shown in FIG. 3, Japanese National Publication No. 2002-525533 of International Application discloses a needle roller bearing 6 which comprises an outer ring 7, a plurality of needle rollers 8 arranged on an orbit surface of the outer ring 7 so that they can roll thereon, and a cage 9 holding the needle rollers 8 at intervals. When the needle roller bearing 6 supports a shaft, the cage 9 is prevented from being shifted in an axial direction by reducing an axial diameter at both ends of the bearing of the shaft 5 so that the cage 9 protrudes inward along a diameter.
Since load is deflected to a predetermined direction in the crankshaft 1 shown in FIG. 1 and the like during rotation, the outer ring of the bearing comprises a region in which the load is concentrated (referred to as the “load region” hereinafter), and a region in which great load is not applied (referred to as the “non-load region” hereinafter). Thus, when the outer ring of the needle roller bearing 3 shown in FIG. 2 is set in the shaft, a boundary 4c of the outer ring members 4a and 4b is to be positioned in the non-load region.
However, since the outer ring members 4a and 4b are only fixed by being fit in a housing, when the roller bearing 3 receives load during the rotation, the outer ring members 4a and 4b could be rotated and displaced in the housing. At this time, when the boundary 4c of the outer ring members 4a and 4b is moved to the load region, a rotation defect of the needle roller could be caused or the outer ring members 4a and 4b could be damaged and the like.
In addition, according to the needle roller bearing 6 shown in FIG. 3 and the like, since a process for the shaft 5 to prevent the cage 9 from being shifted in the axial direction is needed, its processing cost is increased.